The hydrocarbon processing industry needs
reliable and economic sources of water for present and future
operations. Ensuring a sustainable water supply requires a
focused effort to evaluate the quality and
quantity of alternative water sources, reuse of
individual water streams or the combined outfall stream, and/or
changing regulatory requirements.

Modeling

The most common methodologies to analyze water circuits are
pinch technology and mass balance/solution
modeling. Application of classic pinch technology for water systems, as
shown in Fig. 1, evaluates only the hydraulic
demands for water.

Fig. 1. Sample
water-pinch diagram.1

Better option

A better solution is to construct a sophisticated
computerized model of the facilitys water systems that
incorporates hydraulic information, along with ionic equilibria
of soluble contaminants. Like pinch technology, this approach requires
an accurate water balance.

Fig. 2 is a sample flow diagram with
color-coded streams: steamsred, waterblue, recycled
watergreen and wastewaterbrown. This approach
models the ionic equilibria of the soluble contaminants,
providing information about water quality for each unit
operation.

Modeling a water system also requires creating a
salt or contaminant balance. The optimal approach
is to profile water quality throughout the system by analyzing
numerous samples at every location, and then compare the actual
water quality to the predicted value in the model. When the
actual water quality and flowrates closely match the predicted
values, the model is considered validated for the
present plant conditionsthe baseline case.

A validated model allows the facility to hypothetically
reprocess water to meet the specification limits for individual
process units and to identify candidate water streams for reuse
or retreatment (recycling). The model also provides insight
into the hydraulic and chemical impacts on the unit and the
total system balances for mass and salt concentrations.

This computerized modeling provides an accurate assessment
of options: different configurations and/or operating scenarios
to improve system operability, justification capital
improvement projects, optimization system reliability and minimization of the
risk of off-spec or lost production. Embedded within this
analysis is a projection of the chemistry change
for the cooling water. The only remaining analysis for this
unit operation is a separate modeling task using a different
software program to design an appropriate chemical-treatment
program to control the corrosion, deposition and
microbiological populations within the cooling water
circuit.

Quality repurposing

As the quantity and quality of water decreases, industrial
users will need to increase their efforts to conserve, recycle
water and conform to even stricter regulatory requirements for
withdrawal and discharge. Software tools can provide methods
for plant personnel to quickly and economically analyze
numerous system configurations providing a high level of
confidence about the option that best meets their
objectives.

Loraine A. Huchler is president of
MarTech Systems, Inc., a consulting firm that provides
technical advisory services to manage risk and optimize
energy- and water-related systems including steam,
cooling and wastewater in refineries and petrochemical plants. She
holds a BS degree in chemical engineering, along with
professional engineering licenses in New Jersey and
Maryland, and is a certified management consultant.

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